The invention relates to a method for testing whether planar material, in particular films, are leakproof, in which the planar material is continuously conveyed through a test chamber, and to a device for carrying out this method.
Planar materials such as, for example, films, which are free of tears and holes and are thus gas-tight, are known to be required in numerous technical fields. For example, gas-tight films are required when manufacturing fuel cell stacks such as are used in fuel cell vehicles. For this purpose, the films are tested for gas-tightness after their fabrication.
In order to test whether planar materials are leakproof, electrical test methods are known which, however, cannot be applied to electrically conductive films, for example.
U.S. Pat. No. 3,937,064 describes a continuous method and a device for testing whether a diaphragm strip is leakproof. For this purpose, the diaphragm strip is unrolled from a first roller and rolled up again by a second roller. Between these rollers a test chamber is arranged in which a test fluid is applied on the upper side of the diaphragm strip. By means of a pressure difference which can be set in a defined fashion the test fluid is forced through the diaphragm strip, by way of a capillary effect at holes if they exceed a certain size so that said test fluid leaves behind a mark on a detector surface of a detector belt which is guided along in parallel with the diaphragm. The test fluid is fed via a distributor pipe which is embedded in a foam rubber block which is arranged transversely with respect to the direction of conveyance of the diaphragm strip, in order to apply the test fluid uniformly and to protect the diaphragm strip against damage.
U.S. Pat. No. 3,857,278 describes a method and a device for testing the tightness of sealed containers. For this purpose, the containers are fed through a tunnel-like chamber on a conveyor belt. At the start and end of a tunnel section of this chamber a carrier gas is fed into the chamber and the gas flows partially into the tunnel section and partially in the opposite direction. The carrier gas which flows into the tunnel section flows past a container to be tested and is then led out again via a branch and examined for impurities owing to a leak in the container.
U.S. Pat. No. 5,889,199 describes, for the purpose of testing whether a container is leakproof, a device with a test head which has two tubular ducts, one of these ducts being arranged inside the other. At a test point on the container to be tested, gas for analysis is fed into the device through the inner duct by means of a partial vacuum, while at the same time a selectable environmental gas flows out of the outer duct so that the test point is closed off from a possible other environmental gas.
Laid-open German patent application DE 196 05 920 A1 discloses a device for testing whether ceramic plates are leakproof. For this purpose, the plates are clamped in the device and a test gas is applied to them on one side.
If there are leaks in the ceramic plate, the test gas is forced through it as a result of overpressure and is registered on the low pressure side by a detector.
Laid-open patent application WO 02/088657 A2 describes a method and a device for investigating products from a polymer material such as, for example, films and bottles in terms of their permeation and desorption rates. The polymer contains for this purpose a first isotope of a test gas and a second isotope of the test gas is used on one side of the product. On the other side of the product, the concentration of both isotopes of the test gas is then measured separately.
The object of the present invention is to specify an improved device and an improved method for testing whether planar material is leakproof, in particular with respect to the supplying of the planar material to a test chamber, and its discharging therefrom, as well as the conduction thereof within this test chamber.
In the method according to the invention, a planar material is continuously conveyed through a test chamber in a continuous process. As a result of the continuous conveyance, planar materials, such as films, with virtually any desired size can be examined to determine whether they are leakproof. The test chamber contains, on opposite sides of the planar material which is being conveyed through, a test gas chamber to which test gas is applied, and a measuring chamber which is monitored for the presence of test gas. As a result, all the conceivable materials, even electrically conductive materials, can easily and reliably be tested to determine whether they are leakproof. The test gas chamber and/or the measuring chamber are sealed at a test chamber inlet duct and/or a test chamber outlet duct for the planar material which is to be tested by means of a gas curtain whose gas pressure is higher than the gas pressure in the test gas chamber or the measuring chamber. This avoids the situation in which the test gas flows, for example, out of the measuring chamber before it is detected. The seal, which is to this extent contact-free, avoids any risk of damage to the film such as occurs with a tactile seal.
The device according to the invention has a test chamber and means for continuously conveying the planar material through the test chamber, with the test chamber comprising a test gas chamber and a measuring chamber on opposite sides of the introduced planar material. In the case of the device, the test gas chamber and/or the measuring chamber has an open-pore material which contains in each case a planar surface, which is continuous from a test chamber inlet to a test chamber outlet on the side of the planar material. This open-pore material is used in the test gas chamber, on the one hand, for guiding the material to be tested as it is conveyed through the test chamber, and on the other hand, the open-pore quality ensures an even application of test gas. In the measuring chamber, the material has the purpose of supporting the surface material to be tested.
In one development of the invention, the inlet duct and/or the outlet duct are bounded by in each case two compressed gas chambers which lie opposite one another and which generate the respective gas curtain by means of a compressed gas, for example, compressed air. In one refinement of this measure, an open-pore material is introduced at least into one of the compressed gas chambers. This open-pore material serves primarily for guiding the planar material which is introduced. In addition, the open-pore quality ensures that the compressed gas passes through uniformly in order to generate the gas curtain.
In another development of the invention, the device has a vacuum pump which is coupled on the suction side to the measuring chamber. As a result of this vacuum pump it is possible for test gas which passes into the measuring chamber if there is a leak in the planar material to be reliably directed to the test gas sensor system.
In yet another development of the invention, the device has a computer-supported image processing system for coarse leak detection on the inlet side of the test chamber. By means of this image processing system it is possible to detect relatively large leaks in the planar material before the material enters the test chamber. This makes it possible to prevent material to be tested with relatively large leaks from entering the test chamber and to prevent the measuring chamber from being contaminated with too much test gas.
One advantageous embodiment of the invention is illustrated in the drawing and will be described below.